1. Field of the Invention
The invention relates to the formation of articles using a breathable, electromagnetic shielding material. More particularly, the invention pertains to a material and process for the formation of articles capable of shielding electromagnetic waves while allowing the release of thermal energy.
2. Description of the Related Art
Electromagnetic radiation is formed from a combination of electric and magnetic fields generated by the movement of electrons through conductors. Certain electronic devices, such as radios or televisions, may utilize electromagnetic waves by intercepting transmitted signals. It is also well known that the performance of some electronic devices, or devices having electronic components can be negatively affected by the influence of electromagnetic wave radiation surrounding such devices. For example, electromagnetic waves may affect the operation of computer chips, sensors or various electronic detectors.
To combat this problem, it has been known in the art to develop structures or materials that are capable of shielding electromagnetic waves penetrating certain devices. For example, U.S. Pat. No. 6,054,647teaches a nickel coated, woven grid material for incorporation with a molded housing to provide electromagnetic and radio frequency shielding. U.S. Pat. No. 5,310,784teaches a composite carbon-resin reaction compound prepared by mixing a polymerizable resin with a carbon powder and polymerizing the mixture. The composite is capable of being readily formed into any configuration of a device housing. U.S. Pat. No. 5,989,720 teaches an electromagnetic wave shield material composition comprising a mixture of silicone resin, baked ceramics material and a mixture of an aluminum powder and/or stainless metal powder.
While these known structures or materials may be useful for preventing the penetration of electromagnetic waves into an electronic device, they also have the adverse effect of preventing heat generated by such electronic devices from being released. It is well known that along with being negatively influenced by electromagnetic radiation, the performance of electronic devices may be affected by prolonged heat generated during their use, such as by permanently damaging parts within the device or causing the device to malfunction. In addition, the buildup of heat within the device may also reduce the lifetime of the electronic device. It is therefore desirable to have a material for forming electronic devices or electronic components for electronic devices that allows for heat to be released from the device as a cooling mechanism, while also blocking the entrance of harmful electromagnetic radiation. The present invention provides an alternative to these techniques above.
The present invention provides an electromagnetic shielding material comprising an arrangement of thermoplastic polymeric fibers infused with particles of an electromagnetic shielding powder. The polymeric fibers used herein are multilobal fibers disclosed in U.S. Pat. Nos. 5,057,368 and 5,744,236. The fibers are extruded and either woven together or arranged into a non-woven structure, and the powder particles are physically deposited within cavities formed by the fiber lobes and between fibers, forming a flexible shielding material. The flexible material may then be cut or formed into a structure of generally any shape or form and used as a housing for an electronic device. The material is breathable, in that it allows for the dissipation of non-linear thermal energy generated by a device, while preventing linear electromagnetic waves from entering the device.
The invention provides a process for forming a flexible, breathable electromagnetic shielding material for forming electromagnetic shielding articles comprising:
(a) forming a molten thermoplastic polymer mixture comprising one or more polymers;
(b) melt spinning said polymer mixture to form a plurality of multilobal fibers, said fibers comprising a central core having a plurality of T-shaped lobes projecting therefrom, each of said T-shaped lobes having a leg and a cap, said lobes defining a longitudinally extending internal cavity between two adjacent legs that extends the entire length of the fiber;
(c) arranging together said plurality of multilobal fibers into a sheet, the sheet having at least one surface; and
(d) applying electromagnetic shielding powder particles to at least one surface of said sheet to infuse said electromagnetic shielding powder particles between said multilobal fibers and into each cavity, said powder particles being of such a size, shape and makeup that they are securely retained within each cavity.
The invention also provides a flexible, breathable electromagnetic shielding material for forming electromagnetic shielding articles comprising:
(a) a plurality of polymeric multilobal fibers arranged together into a sheet having at least one surface, said fibers comprising a central core having a plurality of T-shaped lobes projecting therefrom, each of said T-shaped lobes having a leg and a cap, said lobes defining a longitudinally extending internal cavity between two adjacent legs that extends the entire length of the fiber; and
(b) electromagnetic shielding powder particles infused between said arranged fibers and in said cavities, said powder particles being of such a size, shape and makeup that they are securely retained within each cavity.